• You can use 9 inch round bamboo steamer. If you use 8 inch, the cake will be taller and steaming time need to be longer too. I highly recommend using a bamboo steamer lined with parchment paper to steam the cake. The bamboo basket has holes at the bottom and the cake cooks better that way and you won't have dense spot. Regular cake pan will work too, but if you have a bamboo basket, I would use that instead
  

Prepare the levain:

• Prepare the levain at 1:1:1 ratio. If you prepare overnight, you can try using 1:5:5 ratio for example 14 grams active starter + 70 grams water + 70 grams all-purpose flour. This will take about 8-10 hours to peak at 75-78 F (24-26 C). This depends on the temperature, the warmer it is, the faster it peaks.
  
• If you want to use unfed sourdough discard, I suggest it is within 48 hours. Simply bring the discard out from the fridge to sit at room temperature while you gather your ingredients. If your discard is older than 48 hours, I suggest adding 1 teaspoon of instant yeast

Prepare the cake batter:

• It is best to use eggs and milk at room temperature. I usually let them sit out for about 30 minutes at room temperature
• Whisk the eggs, salt, and sugar vigorously until the sugar dissolves.
  
• Add the sourdough starter
  
• Whisk again to loosen up the starter until it combines. Add the milk and vanilla and whisk again to combine
  
• Sift in the cake flour. Use a whisk to combine.
  
• The batter may be lumpy. Strain the batter
  

Proof the cake batter:

• Cover the bowl and let the batter proof at a warm place (about 82 F/28 C) and let the batter proof until you see lots of tiny bubbles on the surface, about 2 1/2to 3 hours at the mentioned temperature. The sourdough version won't be as foamy and bubbly compared to ma lai gao made with yeast
  

Prepare the baking soda and baking powder mixture:

• Fill your steamer with water and bring it to a boil. You want to fill it up with enough water but not too much that the water touches the bottom of the basket you are steaming the cake in, causing the bottom of the cake to be wet and has a dense layer
• Whisk oil, baking soda and baking powder in a bowl. Use a whisk to gently stir the cake batter after proofing. Scoop about 4 tablespoons of the cake batter into the oil mixture
  
• Whisk vigorously to combine. We do this so that the consistency of the oil is similar to your fluffy cake batter so they mix much easier
  
• Pour the oil mixture into the cake batter.
  
• Use a spatula or a whisk to swipe down and fold again to combine thoroughly
  
• Pour the cake batter into a prepared bamboo steamer or cake pan.
  
• Put some thin slices of almond or melon seeds on top if you like. I use white sesame seeds this time
  

Steaming:

• If you don't use a bamboo steamer, make sure you wrap the lid of the steamer with a cloth to prevent water condensation from dropping on the cake surface. If you use a bamboo steamer, you won't have this problem
  
• Steam on high heat for 45 minutes if using 8-inch round bamboo steamer and about 35-40 minutes if using 9-inch. If using metal cake pan, add another 5 minutes or so.
• A cake tester inserted into the center of the cake should come out clean with a few crumbs is okay, but it shouldn't be wet and sticky. If it is, steam another 5 minutes and check again
  
• Remove from the steamer. Let them cool down a little bit and then lift it out from the basket or pan onto a cooling rack so the bottom won't get soggy because of condensation trapped underneath. Serve the cake warm or at room temperature